Hello, Note : when Firefox gives you the prompt to set it as the default, it will open the settings in which you have to set it. If not, it will not change to Firefox. If you have the PDF files on your computer, you can : Right click the file, and select open with, and choose Firefox. Also, when doing so, check the box that says '''Always use this app to open .pdf files'''. If not, you can try repairing edge. Open Control Panel > Programs and Features, find Microsoft Edge, then click change. after that, click repair. after the repair, make sure to set Firefox as the default again. since you have the pro version, you can also go to '''services.msc''' and find '''gpedit.msc''', then set default associations.